To promote the flexible use of a firearm, it is often desirable to attach and secure accessories to the firearm. In particular, with tactical rifles, such as the M-16, or its civilian counter-part the AR-15, it is generally desirable to attach flashlights, sights, lasers, scopes, scope rings and the like. Most accessories are attached via a rail system employing what is referred to as the M1913 Picatinny standard, i.e., a Picatinny rail. Typically, the point of attachment for such a rail is either the upper receiver of the firearm or the hand guard which surrounds the barrel and protects the hands of a shooter from heat.
Many known rail systems include an accessory rail that is integral with a hand guard. Such hand guards are either secured to both the barrel nut and the top of a firearm receiver or are attached only to the nut. As discussed below, however, these known systems have potential drawbacks.
Several known designs involve the radial attachment of a hand guard rail system to a conventional barrel nut through a clamp or a yoke while floating about, i.e., not touching, the barrel. An example of such a design is shown in a patent to Troy, U.S. Pat. No. 7,216,451. In general, these designs permit the hand guard to twist or move laterally relative to the receiver when the guard is jarred or bumped. This potential for movement is due to the large moment arm created by the extension of the relatively long hand guard from the barrel nut, in combination with the flexibility of, and motion between, the intermediate pieces connecting the hand guard to the receiver. Such movement is potentially problematic if, for example, sights or scopes are mounted to the rail.
Other somewhat similar designs allow a hand guard rail system to be attached to a barrel nut through the use of setscrews. For example, a patent to Booth, U.S. Pat. No. 6,671,990, discloses a hand guard including an adaptor ring, which is slipped over a barrel nut and secured via a series of setscrews. Setscrew arrangements, like clamp or yoke arrangements, potentially permit movement of a hand guard relative to a receiver upon jarring.
A more recent design is disclosed in a published patent application by Daniel, et al., US 2008/0092422, which is directed to a hand guard and accessory mounting device for a firearm. This design includes an adaptor that mounts between the barrel nut and a portion of the firearm, as opposed to the hand guard being clamped directly onto the barrel nut. A problem with this design is that it is difficult to precisely align the top rail surface of the hand guard with the top of the firearm upper receiver so that they are in registration. Indeed, alignment is accomplished through trial and error by placing the adaptor in an estimated aligned position, securing the adaptor via the barrel nut, and then assembling the rail/hand guard to the firearm to assess alignment. Threading the barrel nut onto the receiver to secure the adaptor can cause rotation of the adaptor from its aligned position, which rotation could be detectable only by assembling the rail/hand guard to check alignment. If misaligned, the rail/hand guard must be disassembled and realigned. Moreover, the hand guard in US 2008/0092422 is relatively expensive to manufacture. This cost is due in large part to the number and variety of CNC machining setups required to cut internal and external surface features of the guard.
Another recent class of designs is typified by a published patent application by LaRue, US 2007/0017139, which discloses a hand guard/barrel nut clamping assembly for a tactical firearm. The assembly includes a barrel nut that is received within an annular hand guard retainer nut. Additionally, an anti-rotation clamp plate is employed to prevent the nuts from rotating relative to one another. Not only do additional components render such designs relatively expensive to manufacture, but also, the barrel nut is difficult to access for attaching or removing a barrel to or from the firearm. Moreover, while the anti-rotation clamp may prevent gross rotational movement of the nuts/hand guard after assembly, it still allows for rotation of the nuts during assembly and also allows for a small degree of rotation between the hand guard and the upper receiver after assembly.
As exemplified by the Daniel and LaRue designs, a problem with known hand guard rail systems is that the hand guards are manufactured from a substantial amount of material and have a fairly complex geometry. In particular, the rail portions of the guards are quite thick and the geometry of the guard surfaces requires extensive CNC machining. As will be appreciated, it is desirable to manufacture a hand guard rail system that is of a lighter weight and requires minimal CNC machining while maintaining sufficient strength and rigidity.
With the foregoing concerns in mind, it is the general object of the present invention to provide a hand guard rail system that is easily aligned and is resistant to rotational movement relative to a firearm receiver. Moreover, it is an object of the present invention to provide a strong, lightweight hand guard rail system that may be easily and inexpensively manufactured and assembled.